The invention generally relates to an energy absorbing damping device for safety belts of motor vehicles, and more particularly to such a device which, despite its small construction, has a high energy absorption capacity with good reproducibility of results.
In the event of an accident, safety belts of motor vehicles are plastically and elastically deformed by the kinetic energy of the secured belt user. The elastic extension of a safety belt is undesirable, as it causes the belt user to be thrown backwards after the extension of the belt in such a manner that injury can result. However, the plastic deformation of a belt also damps the impact during the accident.
This deformation is subject to narrow limits as a result of the nature of the belt strap. For this reason, a provision has already been made for providing the safety belt with an additional damping device. When a given maximum force is reached, this damping device absorbs energy, by plastic deformation or distortion of a strip element, and thus causes a damping of the deceleration effect.
In this connection, U.S. Pat. No. (US-PS) 4,027,905 discloses the provision of guiding a strip element in a serpentine manner around deformation members in the form of bolts or bars which are arranged at a distance one after another. In the event that the strip element is pulled out as a result of an accident, the strip element is alternately deformed, the last deformation member in the pull-out direction once more straightening the strip element.
In the deflection process performed by the bolt or bar-shaped deformation members of the above-noted patent, a high degree of friction arises, which, as experience has shown, results in poor reproducibility of the desired damping. This poor reproducibility is further worsened by the fact that a change takes place in the originally planned frictional force as a result of dust which builds up in the course of time. It is also disadvantageous that, in order to achieve a high energy absorption capacity, several bolts or bars have to be arranged one after another and as a result a large construction length is obtained.
An object of the present invention is to provide an energy absorbing damping device which, in spite of a small construction size, has a high energy absorption capacity with good reproducibility of results.
In the damping device according to preferred embodiments of the present invention, the energy absorption is effected in that a strip element passes between two deformation members in a first operation and undergoes a first sectional deformation with a high degree of deformation, during which it is shortened. In a second operation, which follows immediately, the strip element is once again pulled straight, that is to say lengthened, with further energy absorption. As a result, an optimum shock absorption effect is achieved, which can then be adjusted to differing circumstances if the size of the deformation forces during the pulling-out process of the strip element are controllable, in particular reducible.
In this connection, German Patent Specification No. (DE-PS) 2,249,759 discloses the provision of purposefully changing the retention force of a belt force limiter as a function of certain basic conditions.
In a preferred exemplary embodiment of the invention, a bearing bolt of at least one toothed roller is arranged transversely displaceably to a pull-out direction of the strip element. An adjustment member engaging on the bearing bolt is provided in order to displace it. German Published Unexamined Patent Application No. (DE-OS) 2,200,565 discloses the provision of displacing, traversely to the passing-through direction, a brake block, which acts upon a strap which passes through the brake block and is guided in a serpentine manner so that an automatic return displacement takes place with increasing pull-out force. However, as a result of interconnected springs, it is not possible to provide a deliberately affected control movement for the prevention of the appearance of a force peak at the beginning of the crash.
In a further embodiment of the present invention, the strip element has three sections, of which a central section has a constant width over a length thereof. A section extending towards a pulled end decreases degressively in its width, over its length, from the constant width of the central section to a free end. A section extending towards the other end decreases linearly in its width, over its length, to the constant width of the central section. On account of the fixed size of the differing deformation cross-sections, the retention force of the damping device in a corresponding section of the strip element can be predetermined.
A reference to providing a strip element, which can be pulled out while absorbing energy, with sections of differing widths is made in U.S. Pat. No. (US-PS) 4,027,905, although in this case, on account of the initially large cross-section, an unfavorable force peak must be expected at the beginning of a crash.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.